The feasibility of applying Optical Backscatter Reflectometry as a backface strain monitoring method for bonded joints subjected to mode I fatigue crack propagation was studied. Visual evaluation and Digital Image Correlation methods were applied to track the crack-tip position and the onset of plasticisation in the adhesive, respectively. The methods were compared to understand the relationship between the changes in the optical fibre measurements and the crack propagation. The absolute maximum strain values gave important information about the crack propagation stage (stable or high velocity) within the adhesive and fast-rate crack propagation, which resulted in a sudden increase in strain values. Finally, the strain peak position was found to be a valuable indicator of crack tip position.